Abstract: The invention is a method of reducing formaldehyde emission from wood-based composite boards bonded with aminoplast resins. A salt mixture comprising urea, or one of its analogs, a readily decomposible ammonia liberating compound and, alternatively, a resin catalyst is prepared in a finely granulated form. This is then added to the dried wood particles and blended, preferably prior to the addition of the adhesive binder resin. The salt mixture comprises 12-20 parts of the ammonia liberating compound, 65-88 parts of urea or its analog, and 0-15% of the catalyst. From 6-22.5% by weight of this mixture is used, based on resin solids. Formaldehyde evolution is reduced by 45-80% compared with untreated particleboard without adverse effect on physical properties or press time.